1. Field of the Invention
The present invention relates to a solenoid, and more particularly to an electromechanical solenoid having an alignment member for alignment of two pole pieces between which an armature moves.
2. Description of the Related Art
An electromechanical solenoid is a device that converts electrical energy into linear motion. Solenoids are used in a vast array of applications due to their utility. For example, solenoids are commonly used to control mechanical devices, including valves. In this application, the solenoid is typically mechanically coupled to the valve, either a pneumatic or hydraulic valve, and the solenoid is used to actuate the valve.
Referring to FIG. 1, solenoid 30 includes an electromagnetic coil 32 wound around an annular bobbin 34. An induced magnetic circuit travels through pole pieces 36 and 38, and a moving armature 40. A ferromagnetic housing 42 completes the basic magnetic circuit.
A common arrangement for creating and maintaining alignment of components within a solenoid is through the use of a non-magnetic cup-like tube 44 as seen in FIGS. 1 and 2. There are several tube arrangements that can be either open or enclosed, but the fundamental purpose is the same. The tube 44 provides a uniform smooth surface 46 for the armature 40 to travel, thus reducing hysteresis in the force output of the solenoid 30. The tube 44 is typically made of a non-ferromagnetic material such as stainless steel or aluminum. It may also be post treated to improved durability from the armature traveling against its surface.
Referring to FIG. 2, this common solenoid arrangement results in losses in the magnetic circuit due to air gaps, such as 48 and 50. These losses due to the air gaps are not desirable because they take away force from the solenoid output. One of the primary losses in current solenoid arrangements is due to the non-magnetic cup-like tube 44, which creates an additional air gap between the armature 40 and the pole piece 36. However, elimination of the tube 44 results in uncontrolled axial alignment of the armature 40 within the solenoid, which creates hysteresis in the force output of the solenoid.
Thus, maintaining alignment of pole pieces and reducing non-working air gaps becomes an important element in the improved operation of an electromechanical solenoid.